The problem is surely the antivirus.
At the end of the installation, the installer starts Couatl in "test mode", to see if it works. The test mode doesn't do *anything* other than just starting, doing nothing and exit.
Since it's not possible a program would crash without having done anything, the only possible reason is the antivirus blocking or corrupting it, trying to "heal" it from a non-existent threat.
You can also try the Couatl test mode manually, by doing this:
- Open a command prompt ( Start->CMD->Enter ) and go to the Addon Manager\Couatl folder
- Type the following:
Couatl.exe --test
If there's a problem with missing system libraries, you might see some kind of error from Windows, saying something about it.